Rate of change of blood pressure in premature and full term infants from birth to 4 months

Systolic and diastolic blood pressures were evaluated in a cohort of 61 non-hypertensive premature [very low birth weight (VLBW), n = 16; low birth weight (LBW), n = 22] and full-term [normal birth weight (NBW), n = 23] newborn infants admitted to a neonatal intensive care unit (NICU) and followed to their 4-month age-adjusted outpatient examination. All were receiving routine postnatal care by 7 days of age. Blood pressure was measured at 7 days of age, at discharge from the NICU, and at the outpatient examination. Simple linear regression of blood pressure on weight was used to fit a straight line to the three measurements for each infant and the average regression line for each birth weight group was then obtained. There was a significant correlation between systolic, blood pressure and both weight and length at each of the measurement points and also between the change in systolic, blood pressure and change in weight from the discharge to the 4-month examination. Diastolic blood pressure tended to follow this same pattern. Gestational age was correlated significantly with the 7-day blood pressure, but postnatal age at the outpatient examination was not correlated with either systolic or diastolic blood pressure. The average slopes of systolic and diastolic blood pressure on weight (mmHg/kg body weight) were virtually identical for the LBW and NBW groups; in contrast, the average slope of the VLBW group was greater than the other two groups, and the difference was statistically significant for diastolic blood pressure. These results show significant group differences in mean blood pressure prior to 4 months of age between VLBW, LBW, and NBW groups and, for the VLBW infants, a steeper slope of the estimated regression line of blood pressure on weight between birth and 4 months.